The airport is called ELEFTHERIOS VENIZELOS.

If you have past experiences of the old airport consisting of two terminals then you will love this
modern, European airport.
If its your first time to/through Athens airport then you lucky thing - for not having experienced the previous airport.

The Eleftherios Venizelos is now on par with most European airports - its just one building - with the arrivals and departure areas under one building.
They are obviously on different levels.

It is well sign posted with lots of space to feel lost unfortunately. But you wont be !
Follow the signs from one part to the other and you will be fine.

Security is very strict and so it should be. Be prepared to be searched and to have your hand luggage scanned and searched.  There are new LIQUID regulations now so be aware of them before you check-in.

There are several shops and restaurants within the check-in are and within the passport control area.

On arrival, walk out of the luggage area and follow the signs for the METRO.
They will lead you out of the arrivals building, across the road and towards the SOFITEL hotel. 
Next to that is the METRO station.  Escalators will take you the the station itself where you will need
to buy a ticket for your destination.

 You must validate your ticket(s) in the small vertical 
 machines which you need to pass to go down the escalators 
 to the train platform.